Rengoku was not merely a technique. He represented an unwavering combat will and a profound understanding of flame itself.
To fully absorb the essence of Flame Breathing, Raiden had to abandon reliance on his other breathing styles and immerse himself completely in the inferno. Only by doing so could he grasp its true nature.
After a long stretch of pain and resistance, he finally brushed against the core of Flame Breathing. It was a power where destruction and renewal existed side by side, where the end of something old gave birth to something stronger.
In that moment, Raiden understood.
He let himself merge with the flames.
When the integration ended, Raiden opened his eyes. Faint embers flickered within his pupils.
"Hoo… that feels good."
He exhaled deeply. The fusion had been even more punishing than Rock Breathing, yet the sensation afterward was remarkably invigorating.
The scorching energy within him was now calm and obedient, a sharp contrast to how violently it had resisted him during the process.
Raiden rose to his feet and picked up his nichirin blade. Taking a steady breath, he guided the newly integrated Flame Breathing through his body and into the sword.
The blade, once glowing with the golden hue of Thunder Breathing, began to change.
The lightning faded, replaced by a deep crimson glow.
The color intensified until flames seemed to coil along the edge, reflecting against Raiden's pale features and white hair.
Only now did he fully sense the difference between the two breathings within him.
Thunder Breathing granted speed and explosive force.
Flame Breathing offered endurance and overwhelming destructive power.
Yet they did not repel each other.
There was a subtle connection between them.
Raiden had noticed it earlier, during the initial stages of fusion. The moment Flame Breathing awakened, it had instinctively gravitated toward Thunder Breathing.
Could the two be combined?
Thunder and flame.
The idea lingered in his mind. The more he thought about it, the more possible it seemed. Perhaps no swordsman had ever merged two breathing styles before, but that did not mean it was impossible.
He set the thought aside for later and focused on the changes within himself.
With a light swing of his nichirin blade, crimson arcs sliced through the air, leaving flickering trails like living fire.
Each strike felt sharper than before. Heat followed every movement, enough to scorch flesh and ignite the air around the blade.
If he had possessed this level of Flame Breathing earlier that day, Sanemi Shinazugawa would never have dared to take his attack head on.
After integrating both Flame and Rock Breathing, Raiden felt his body standing at a new threshold.
Something inside him was close to breaking through.
The barrier holding him back felt thin, fragile, like it would give way with the slightest push. Even without fusing Wind Breathing, he suspected the change would happen tonight.
Every new breathing form strengthened him in different ways, and the effect depended heavily on the source.
If he were to fuse techniques from Tanjiro or Zenitsu again now, the improvement would be modest.
But techniques obtained from the Pillars were different.
They did not just grant mastery over a form, they pushed his overall strength forward in massive strides.
"Next," Raiden muttered.
[Do you wish to fuse Wind Breathing Sixth Form, Black Wind Smoke Haze (Mastery) now?]
[Yes]
Having endured the previous two fusions, Raiden braced himself for pain.
But it never came.
The moment Wind Breathing entered his body, a light and flowing force spread through him, gentle and effortless.
It felt like standing beneath swaying branches, the wind guiding rather than crushing.
As the integration continued, Raiden sensed his body becoming lighter. His movements grew sharper, more fluid. The heaviness Rock Breathing had instilled was softened, refined.
With every breath, he felt connected to the surrounding air, capable of influencing it with subtle intent.
As the vortex of Wind Breathing formed within him, Raiden's awareness slipped into it.
For a fleeting moment, he felt like the wind itself.
Then, something familiar surged through him.
It arrived suddenly, unmistakably clear.
Raiden felt his understanding of breathing techniques rise all at once, as if an invisible force had nudged his inner limits forward.
"Did I break through already?"
He froze, then quickly understood.
Moments like this were rare. They marked true growth, born from insight rather than effort alone.
Usually, such breakthroughs came with strain or resistance.
This time, there was only release.
Wind Breathing gave him a sense of freedom, allowing the change to occur naturally.
Soon after, the integration completed.
Just as Raiden prepared to stand and test his new state, his thoughts grew hazy. Within the blur, several faint lights emerged, drifting upward.
As they brightened, Raiden sensed his overall strength rising again.
Despite having just crossed into a new level, he could already feel himself approaching the next threshold.
That made no sense.
Among the three breathings he had fused tonight, Flame Breathing should have provided the greatest boost.
Yet Wind Breathing's influence had faded after contributing only a fraction of the growth.
So what caused this?
Raiden turned his focus inward and observed the lights circling within his consciousness.
Five of them.
His breath caught.
Could these represent the five fundamental breathing styles now residing within him?
The realization sent a quiet spark through his eyes.